1. Field of the Invention
The disclosure provides molybdenum and/or tungsten-containing catalyst materials useful for the sour gas shift reactions and methods for using such catalyst materials.
2. Description of Related Art
Synthesis gas, also termed syngas, comprising hydrogen and carbon oxides (CO and CO2) is an important feedstock in the chemical and energy industries. It may be generated by gasification of carbonaceous feedstocks such as coal, petroleum coke or other carbon-rich feedstocks using oxygen or air and steam at elevated temperature and pressure. Gasification can provide an undesirably high ratio of CO to H2. To remedy this, the water-gas shift reaction:H2O+CO→H2+CO2 can be used to consume CO and form H2. Specialized catalysts, such as copper-based catalysts, iron-based catalysts and nickel-based catalysts, are typically used in the water gas shift reaction. However, when the synthesis gas contains one or more sulfur compounds, such catalysts can become inactivated. Accordingly, sulfur-tolerant shift catalysts have been developed, based on, for example, cobalt-molybdenum catalyst compounds. When the water-gas shift reaction is performed in the presence of sulfur impurities, it is known as a “sour gas shift”. Sour gas shift reactions are generally exothermic, and are conventionally allowed to run adiabatically, with control of the exit temperature governed by feed gas inlet temperature and composition. With an increase in temperature, however, undesirable side reactions can occur, particularly methanation. Moreover, unsafe reaction conditions and the possibility of catastrophic reaction runaway increase with increasing temperature. The problem of exothermicity is especially important in cases where the inlet gas stream has a high CO concentration. But more and more technologies used for gasification generate high CO concentration (over 60%), well over the 40% CO concentration at which typical industrial sour gas shift reactions run manageably and safely. To avoid side reactions and unsafe operation, the shift reaction is typically performed with considerable amounts of added steam. However, such steam addition can complicate reaction processes, and the costs of generating steam can be considerable.